Week 3 - Structure and function of blood vessels Flashcards
What is the function of blood?
transport, protection and homeostasis
in order to achieve this, blood vessels are required
What are blood vessels?
Closed system of tubes where blood goes away from the heart to the organs and is returned back to the heart.
What is pulmonary circulation?
blood to the lungs
What is systemic circulation?
blood to the rest of the body
What are the different types of blood vessels?
Arteries
Arterioles
Capillaries
Venules
Veins
What are the layers of a blood vessel wall?
→ Tunica intima (interna)
→ Tunica media (middle)
→ Tunica externa (adventitia)
What is the tunica intima?
→Innermost layer called endothelium
which inc. thin flattened cells, a basement membrane and internal elastic lamina
Smooth to reduce friction
Secrete locally acting chemical mediators
Basement mem. and lamina provide support to cells
Why is important that the tunica intima has smooth cells?
If the wall of the blood vessel becomes rough for any reason, platelets could start to adhere to it, causing a clot.
What is the tunica media?
The middle layer of blood vessel wall
→ Made of muscle and the connective tissue elastin - this accounts for the variation of different vessels in terms of levels of elastin and muscle in their walls.
→ Muscle arranged in circular direction to regulate the diameter of the blood vessel - controlled by SNS.
→ External elastic lamina separates outer layer from middle layer and provides support.
What is the tunica externa?
The outermost layer of blood vessel wall
→ Made of elastic and collagen fibres (elastic for stretch and collagen to provide support).
→ Also contains nerves and vasa vasorum (in larger vessels = blood vessels supplying to BV’s themselves)
→ Helps to anchor the vessel to the surrounding tissue
Features, structure and function of arteries?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- carry blood away from heart under high pressure
- 15% blood volume
- elastic arteries → largest arteries i.e. aorta
- muscular arteries → tunica media smooth muscle and elastin
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima
- tunica media
- tunica externa (arranged longtudinally)
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ distribute blood to major organs
→ elastic fibres enable vessels to stretch
→ muscular art. can adjust blood flow
Features, structure and function of arterioles?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- deliver blood to the capillaries
- approx. 400 million
- terminal end of arteriole, distal most muscle cell forms the pre-capillary sphincter
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima
- tunica media
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ regulate blood flow to tissues + affect blood pressure
→ pre-capillary sphincter regulates the resistance to blood flow
Features, structure and function of capillaries?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- microcirculation from capillaries to venules
- 20 billion → large surface area
- 5% blood volume
- found near every cell in body
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima but NO MEDIA OR EXTERNA
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ permit exchange of nutrients and waste between blood and tissues
What are fenestrated capillaries?
Found in kidneys, small intestine, ventricles of the brain
They have small pores to allow larger molecules to pass through
What are sinusoid capillaries?
Found in liver
They have large pores to allow proteins to pass through
Features, structure and function of venules?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- collects blood from capillaries to veins
- thin walls, 10-50um in diameter
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima
- tunica media, little smooth muscle
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ exchange of nutrients and waste
Features, structure and function of veins?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- returns blood back to heart under low pressure
- thin walls
- 0.5mm for small veins ato 3cm in diameter for larger veins
- can stretch
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima thinner than art.
- tunica media thin
- tunica externa thickest layer (containing collagen + elastic fibres)
- valves - thin fold of tunica intima
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ blood reservoir
→ valves - prevent backflow
What is anastamosis?
A union of branches of 2 or more arteries - alternative route for blood
Why is there no tunica media or externa in the capillaries?
To allow diffusion to take place
Exchange of nutrients and waste products in the tissues.
Allows oxygen into tissues and for carbon dioxide to be returned to lungs
How does venous return occur?
As the veins are a low pressure system, they need assistance to return the blood back to the heart.
They gain assistance through:
→ Skeletal muscle pump - e.g. walking - Skeletal muscle contraction assists with pumping blood back to the heart - valves prevent backflow
→ Respiratory muscle pump - Alternating compression and decompression of veins:
When breathing the diaphragm moves down, reducing pressure in the thorax which increases pressure in the abdominal cavity, compressing the veins so blood moves towards the heart.
What is homeostasis?
A state of steady internal, physical and chemical conditions maintained by living systems for optimal functioning for the organism.
Pre-set normal limits: body temperature, fluid balance, pH, ions (potassium, sodium and calcium) and blood sugar levels.
What does the regular mechanism involve to achieve homeostasis?
Receptor: picks up that things aren’t at correct values → thermoreceptor, mechanoreceptor
Control centre: information enters control centre→ respiratory centre, reninangiotensin system
Effector: target acted on to return to normal state
What is blood flow?
The volume of blood that flows through any given tissue in a given time (mL/min)
Blood flow to individual tissues is dependent on requirements
Speed of blood flow key points?
Speed (velocity) of blood flow is inversely proportional to the cross sectional area.
→ when there is extensive branching, e.g. in the capillaries, the flow is slower however this allows for nutrients and waste products to be exchanged through diffusion
What is haemodynamics?
factors affecting blood flow
